Reaction Injection Molding

n (RIM) This term is usually applied to the process of injection molding of urethane reactants in which the two primary constituents, isocyanate and polyol, are pumped by a metering device into a mixing head from which the intimately mixed reactants are quickly injected into a closed mold. The injection pressure is much lower than in conventional injection molding of molten plastics, enabling the use of inexpensive, light-weight molds. However, the mixing head is a high-pressure impingement mixer in which pressures may reach 14–21 MPa. One mixing head may be used to feed up to ten separate molding presses. One of the largest-volume applications of RIM is the production of exterior automotive parts such as body panels and bumpers. Furniture is another big use. The term Liquid Injection Molding (LIM) is usually applied to the similar process of molding other thermosetting resins such as polyesters, epoxies, silicones, alkyds, and diallyl phthalate resins. The terms liquid reaction...